1. Field of the Invention
The present invention relates to a spectrophotometer that measures color of an object to be measured by specifying the spectral reflection property of the object to be measured.
2. Description of the Related Art
Color measuring methods are broadly classified into two methods, i.e., a spectral colorimetry method (spectrophotometric colorimetry) and a stimulation value direct-reading method. A spectrophotometer performs color measurement using the former method. The spectrophotometer calculates tristimulus values from the spectral reflectance of an object to be measured to thereby determine the color value of various color systems standardized by CIE (International Commission on Illumination) based on these numeral values. The spectrophotometer is basically constituted by a light source that irradiates an object to be measured with light, a spectroscope that diffracts light, and a sensor that receives light. A method in which an LED (light-emitting diode) is used as the light source of the spectrophotometer is widely known. In the method, a plurality of LEDs having different spectral intensity distributions is combined with each other such that the spectral intensity distribution of the light source becomes continuous within the visible light region (see FIG. 3 disclosed in Japanese Patent Laid-Open No. 2000-292259). In the method using a plurality of LEDs, a color value to be measured may undesirably be affected by a shift of the spectral intensity distribution due to variations in the manufacture of LEDs.
In order to avoid the disadvantageous circumstance, there has been proposed a light source configuration method in which a color value to be measured is hardly affected by a shift of the spectral intensity distribution of an LED (see FIG. 10 and FIG. 11 disclosed in Japanese Patent Laid-Open No. 2004-101358). The method enables measurement with high accuracy by giving consideration to the color-matching function or the magnitude of the change in the spectral reflectance of an object to be measured upon selection of the spectral intensity distribution of an LED used for a light source.
However, although the method can improve measurement accuracy in a single spectrophotometer, the method does not consider an instrumental error which is a difference in the color value between a plurality of spectrophotometers, resulting in occurrence of variations in measured values for each device.